# Lupus Vulgaris > Lupus vulgaris for NEET-PG Dermatology: the commonest cutaneous TB in India, apple-jelly nodules on diascopy, tuberculoid histology, SCC risk and ATT. - Canonical URL: https://prepelephant.com/topics/neet-pg/dermatology/lupus-vulgaris - Exam / course: NEET-PG · Subject: Dermatology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-14 - Last updated: 2026-10-14 - Reference basis: Rook's Textbook of Dermatology; IADVL Textbook of Dermatology; Harrison's Principles of Internal Medicine - How to cite: "Lupus Vulgaris", PrepElephant, https://prepelephant.com/topics/neet-pg/dermatology/lupus-vulgaris ## Direct answer Lupus vulgaris is the commonest and most typical form of cutaneous tuberculosis in India, arising from haematogenous spread of Mycobacterium tuberculosis in a partially immune host. It presents as soft, reddish-brown nodules and plaques on the face and extremities that show an apple-jelly colour on diascopy. Histology shows tuberculoid granulomas with little or no caseation and scanty bacilli, so the diagnosis rests on the clinical picture, biopsy and standard antitubercular therapy. ## What you must remember - **Pathogenesis:** haematogenous spread from a distant focus, with lesions driven largely by hypersensitivity to the bacilli rather than by heavy bacterial load. - **Morphology:** soft, reddish-brown to yellow plaques and grouped nodules, which may ulcerate and heal with scarring. - **Apple-jelly colour:** the lesion turns yellow-brown under pressure from a glass slide, a classic bedside sign called diascopy. - **Sites:** the face, especially the nose, cheeks and ears, and the extremities, often in a plaque-like or segmental distribution. - **Histology:** epithelioid granulomas with Langhans giant cells and little or no caseation; bacilli are scanty, so culture and smear may be negative. - **Complication:** squamous cell carcinoma can arise in long-standing lesions, particularly scars and ulcerating plaques, and needs biopsy. - **Treatment:** standard antitubercular therapy under NTEP, usually a six-month regimen, with surgical excision for residual or suspicious lesions. - **Differentials:** cutaneous sarcoidosis, leprosy and discoid lupus erythematosus, separated by diascopy, histology and the presence or absence of follicular plugging. ## A stepwise workup for a suspected lesion A slowly progressive, soft, reddish plaque on the face in a patient from an endemic area should prompt a structured workup. Each step narrows the diagnosis, and no single test is decisive on its own. 1. **Clinical screen:** a slowly enlarging, soft, reddish plaque or nodule with a history of TB contact or constitutional symptoms raises suspicion. 2. **Diascopy:** pressure with a glass slide reveals the apple-jelly colour, which supports a granulomatous nodule. 3. **Biopsy:** histology shows epithelioid granulomas with little or no caseation, and Ziehl-Neelsen staining is requested, though it is usually negative. 4. **Molecular and culture tests:** PCR on tissue for M. tuberculosis has greater yield than culture, and a negative result does not exclude the disease. 5. **Systemic evaluation:** chest radiography, tuberculin testing or an interferon-gamma release assay, and HIV testing as for all tuberculosis patients. 6. **Treatment and follow-up:** antitubercular therapy starts, with biopsy of any non-healing, ulcerating or enlarging lesion to exclude carcinoma. Histology carries the diagnosis when culture is negative, which is the usual situation. The clinician therefore relies on the combination of diascopy, granulomas and clinical context rather than on a positive culture. ## Where the exam catches students Most traps arise from relying on culture or misidentifying a benign-looking lesion. - **Trap:** rejecting lupus vulgaris because culture is negative — **Correct:** few bacilli make culture and smear unreliable, so tuberculoid granulomas and PCR carry the diagnosis. - **Trap:** reading a long-standing plaque as a benign skin infection — **Correct:** lupus vulgaris can turn into squamous cell carcinoma, so non-healing lesions need biopsy. - **Trap:** expecting a positive smear to confirm lupus vulgaris — **Correct:** bacilli are scanty, so smear positivity is low even in a true case. - **Trap:** mistaking discoid lupus erythematosus for lupus vulgaris — **Correct:** discoid lupus shows follicular plugging and atrophic scarring without apple-jelly nodules on diascopy. ## Frequently asked questions ### What is the apple-jelly sign in lupus vulgaris? The apple-jelly sign is the yellow-brown colour seen when a glass slide presses on a lupus vulgaris nodule, a finding called diascopy. It reflects the underlying granulomatous tissue and is a classic bedside clue, although it is not specific to lupus vulgaris alone. ### Why is culture often negative in lupus vulgaris? Lupus vulgaris contains very few tubercle bacilli because the lesion is driven largely by hypersensitivity rather than heavy bacterial load. Histology showing tuberculoid granulomas, together with PCR on tissue, therefore carries more weight than a negative culture. ### Which malignancy can complicate long-standing lupus vulgaris? Squamous cell carcinoma can arise in long-standing lupus vulgaris, particularly within scars and ulcerating plaques. Any non-healing or enlarging lesion in a patient with lupus vulgaris should be biopsied to exclude it. ### How is lupus vulgaris treated? Lupus vulgaris is treated with standard antitubercular therapy under the NTEP, usually as a six-month regimen. Surgical excision may be needed for residual or suspicious lesions, and HIV testing is done as for every patient with tuberculosis.